This invention relates to a mixed-firing burner for use with pulverized coal (hereinafter simply referred to as coal) and heavy oil and utilized in a combustion furnace for use in cement kilns or boilers.
For the purpose of effectively using coal which is more abundantly available than petroleum, there have been used burners which employ exclusive firing with coal (combustion by coal itself) or mixed-firing with coal and heavy oil. In the former type burner, since the length of the flame is long, high combustion temperature can not be obtained with the result that it is difficult to obtain perfect combustion and the efficiency of heat utilization is low. In burners which employ exclusive firing with heavy oil (combustion by heavy oil itself), on the other hand, since the oil burns well and the length of the flame is short, it is possible to realize high combustion temperatures. For this reason, the defects of the burner for exclusive use with coal can be eliminated by firing or burning a mixture of coal and heavy oil.
According to the conventional method for the mixed firing, pulverized coal and heavy oil are blown into the burner through parallelly disposed discrete burners or a mixture in which pulverized coals are suspended in heavy oil is burned. However, where pulverized coal and heavy oil are blown into the furnace through separate burners, due to the difference in the combustion characteristics of the flames of coal and heavy oil, it is difficult to obtain satisfactory combustion state, and where pulverized coal is suspended in heavy oil, it is necessary to incorporate an additive for the purpose of improving dispersion of the pulverized coal and preventing prepicitation of the same, thus complicating the operation and increasing the cost of fuel.